This invention relates to technique for routing calls and other types of connection requests in an IP network.
Traditional telecommunications networks typically use dedicated circuits to carry telephone traffic between facilities. Within such traditional networks, switching systems, such as the 4ESS switching systems used by ATandT, route calls by setting up a circuit that lasts the entire duration of the call and then tearing down the circuit thereafter. For this reason, such traditional networks are commonly referred to as xe2x80x9ccircuit-switchedxe2x80x9d networks.
Increases in traffic and capacity constraints on existing switches within such circuit-switched networks has prompted the development of packet-based networks, and in particular, Internet-Protocol (IP) networks. A typical IP network employs a plurality of routers, such as those manufactured by Cisco, Ascend Communications, Bay Networks and Newbridge, among others, to route data packets representing a call or other connection independently from an origin to a destination based on a destination address in each packet. Present day IP networks of the type described above are characterized by best effort routing. In other words, routing, and particularly, path selection occurs generally without regard to criterion such as class of service. Today, examples of the most prevalent routing techniques in IP networks are the Open Shortest Path First (OSPF) protocol and Border Gateway Protocol (BGP). In the OSPF protocol, for example, routers within the network exchange information with each other by a flooding technique so that each maintains a database of the network topology. Using the information in its stored database, each router selects a path for each packet in accordance with user-established cost metrics that typically require the shortest possible path. Using such cost metrics, each router establishes its routing table accordingly so each router can select a path having, for example, a minimum number of links.
Traditionally, providers of telecommunications services have offered different grades or classes of service based on customer demand. To meet quality objectives for such different grades of service, telecommunications providers, such as ATandT, have employed Class-of-Service routing techniques in traditional circuit switched networks. U.S. Pat. No. 5,392,344, issued in the name of Gerald R. Ash et al., on Feb. 21, 1995, and assigned to ATandT (incorporated by reference herein) describes and claims such a Class-of-Service routing technique. Unfortunately, Class-of-Service routing does not exist with present day IP telecommunications networks. Thus, there is a need for an Internet Protocol (IP) Class-Of-Service routing technique.
Briefly, the present invention provides a technique for routing a call or other connection request between an origin and destination in an IP network comprised of routers connected by links that carry data packets between routers. In accordance with the invention, the routers exchange status messages to identify available paths between the origin and destination. Each path includes at least one outgoing link from one router to another. First the class of service of the call or other connection request is determined. Then a path is selected that has a minimum cost, such as for example a minimum number of hops. Thereafter, a check is made by the originating router or possibly a centralized bandwidth broker, based on flooded network status information, of the selected path as to whether the links from that router forming the path have an available depth (i.e., bandwidth capacity not reserved for other services) for the determined class of service. If the links possess the requisite bandwidth, the router routes the packet over the outgoing link. Otherwise, another path is selected and the step of determining if the links forming the path have the requisite depth is repeated. After an allowed path is found, the IP packets are treated according to their class-of-service designated priority in the queuing discipline used by the routers in the path.